Inlay heater and ring



Feb.6, 1940. D. D. M|zzY ET AL 2,188,915

INLAY HEATER AND RING Filed May 26, 1937 45m $8. INVENTORS.

ATTORNEY.

Patented Feb. 6, 1940 UNITEDSTATES PATENT OFFICE Calif Application ,May 26,

1 Claim.

This invention relates to a dental casting ring, and especially to a ring and a heater therefor, both of which are insertable in a centrifugal or pressure casting machine or the like.

It is common practice in making dental castings of inlays to form a wax model or impression conforming to the shape of the cavity to be filled. After the pattern is removed from'the cavity, it is placed on a sprue pin and then imbeddedin an investment material. When the material is hardened, the Wax is melted out by subjecting the investment material to a sufiicient temperature to melt and permit complete removal of the wax. The result of this operation is that a cavity corresponding to the tooth cavity is formed in the investment material and as such is ready for the gold or other material from which the inlay is to be formed. The sprue hole leading to the cavity of the investment is generally so small that molten metal will not flow freely into it. It is for this reason that pressure or centrifugal force is required to force the molten metal into the cavity. Various devices have been provided for this purpose, but with varying success, as it is usually necessary to transfer the investment material from the furnace or other heating device to the casting machine before the molten metal can be poured. This transfer takes time and very often causes a considerhigh coefficient of expansion or contraction of the molten material. Plainly speaking, investment material should be heated to a point where it is expanded to an amount equal to the shrinkage of the metal when it changes from a molten to a solid state. This obviously will not take place unless the investment material is first heated to bring about the proper expansion and then maintained at that temperature untilthe metal is poured.

The object of the present invention is to generally improve and simplify the construction and operation of dental casting devices of the character described; to provide a combination heater and casting ring which are adapted for insertion in a centrifugal, pressure. or like casting machine; to provide a heater and casting ring which is adapted to be electrically heated directly in the casting machine and maintained at the proper temperature up to the very moment the molten metal is to be cast; to provide a casting ring which is removable from the heater so that a number of casting rings may be prepared and cast one after another in the same heater; to provide a casting ring which will require a minimum of investment able temperature drop in the investment material I which is undesirable, due to the comparatively 1937, Serial No. 144,878

material and from which the investment material and the completed casting, may be quickly and readily removed and further, to provide an electricallyactuated heater which is brought up to the proper temperature in a comparatively short period of time and in which the current consumption is maintained at a minimum.

The invention is shown by way of illustration in the accompanying drawing in which- Fig. l is a perspective view of the heater;

Fig. 2 is a central vertical section of the heater, said view showing the casting ring in position in the heater; I

I Fig, 3 is a side elevation of a sprue former showing the sprue pin and wax pattern mounted thereon; I

Fig. 4 is a vertical section of the inlay ring showing it in position on the sprue former and also showing the investment material after it has may have the appearance of that indicated at 2 in Fig. 3. It is placed on a pin 3 which is known as a sprue pin, and this pin is in turn placed in a rubber plate known as a sprue former which is indicated at t. I Atubular sleeve 6, known as an has been made, the wax pattern is removed and inlay ring, terminates in a rounded head section 1 terminating in an annular flange 8. A thin composition of inlay investment material or the like is poured into the inlay ring from the upper end until it is full, as in Fig. 5, the investmentpainted pattern on the sprue pin and former is gently worked down into the investment filled ring and seated. The inlay ring and sprue former are left until the investment material has set, as in Fig. 5, and the sprue former, together with the pin 3. is removed. This leaves the wax pattern within the investment material as shown at 9 in Fig. 5, and it leaves the passage l0 where the sprue pin has been removed. I

The next "operation in general practice is to place the inlay ring in a small furnace and there heat it until the wax pattern melts and only a small portion of wax flows out of the hole ID. as the rest remains and c'arbonizes on the wall of the mold and leaves a residue. The gold or other melting the wax so that it will flow out is provided. This furnace is best shown in Figs. 1 and 2.'

It has an inner central passage ll to receive the sleeve-like end 6 of the inlay ring, and the upper end of the furnace is concave as shown at l2 to receive the head portion 1 of the inlay ring, and the flange 8 will fit over the upper end of the furnace. The furnace itself merely consists of an inner porcelain sleeve l4 around which is wound a resistance heating element of a suitable character such as shown at l5. Insulating material of a suitable nature, for instance mica sheeting, is placed exterior thereof and the two leads of the heating element are brought to terminals indicated at IT. A metal cylindrical outer casing l6 encloses the heating element and the terminals ll project therethrough and are insulated therefrom. The porcelain sleeve around which the heating element is wound is supported between upper and lower head members l2 and i211 which may be spotwelded or otherwise secured to the outer housing IS.

The type of furnace shown does away with the larger furnaces now in general use. Its current consumption is very low, it assumes the required temperature in a shorter period of time, and furthermore has the advantage that it can be placed directly in a centrifugal, pressure, or like casting machine with the inlay ring mounted within it. In fact, after the inlay ring is removed from the sprue former as shown in Fig. 4 it may be placed directly in the heater or furnace and the two of themplaced in the casting machine. The current is turned on merely by applying a socket such as indicated by dotted lines at I 8. The furnace and inlay ring is maintained in an inverted position until the wax pattern has melted and flowed out, and until the proper temperature is reached, when it is ready for the reception of the molten metal. The wax is completely washed out ofthe mold because the coil first heats up in the center just opposite the wax which is softened and'then washed out immediately by hot water liberated from the investment. No wax is left in the mold to carbonize, and smooth castings result. The current may be maintained on the heater until the very moment the metal is readyto be cast, and it is then only necessary to remove the socket l8 and start the centrifugal casting machine in operation. In pressure machines it is 2,188,915 I a V 7 not necessary to disconnect the socket until after the casting is made. ,All chance of lowering the temperature of the investment material prior to the delivery of the molten'metal is thus avoided, insuring perfect or accurate castings at all times. If a number of castings are to be made, a number of inlayrings may be prepared at one time, and they may be placed in the heater one after another, as when one castinghas been completed, it is only necessary tov remove the inlay ring containing'the'same and replace it with another. Furthermore as the inlay rings are removable with relation to the furnace, cooling the furnace is unnecessary in order to remove the casting, as the inlay ring itself is removable and the casting may be removed there.-

from. The investment ring will be made of a metal, to-Wit, Monel, which has a coefiicient of expansion substantially the same as the invest-- ment material, thereby permitting free expan: sion of said material when heated. Saving of time and current are obviously effected in the use of the machine here shown. The heater, together with the investment ring placed therein, reaches the desired temperature of approximately 1250 Fahrenheit in about fifteen minutes,

the current consumption being only about watts per hour. The amount of investment material required is maintained at a minimum and it is readily removed to liberate the casting. By

referring to Fig. 6, it will be noted that the sleeve 6 of the inlay ring is perforated through-. out its length as shown at 6a. This is also important, as the perforations permit freeescape,

of steam and moisture as the investment material is being heated, thus permitting the investe ment material to dry without any danger of checking or cracking the'investment material.

While these and other features of the'present invention have been more or less specifically described and illustrated, we wish it understood that various'changes may be resorted towithin the scope of the appended claim, and that. the

materials and finish may be such as the experi'-' ence of the manufacturer maydictateand other conditions may demand. v Having thus described our invention, what we claim and desire to secure by LettersPatent is:

In a device of the character described an investment ring comprising an elongated sleeve and an annular flaring head on one end of the sleeve adapted to support and center the sleeve with relation'to a sprue former while. the investment material is being poured into the sleeve,

said sleeve and head being made of a metal hav- 5 ing substantially the same coefficient of expansion 

